Static electricity creates problems in the electronics and other industries, particularly with the advent of integrated circuits and other microelectronic components. Components such as integrated circuits, for instance, may be disabled or destroyed by over-voltages or power density resulting from static electricity. Certain junctions in such circuits can be destroyed by as little as a 50 volt potential, which radically changes the doping structure in their lattices. Power densities resulting from excessive potential and imperfections in circuit layout or structure can vaporize or radically alter the silicon substrate and thus impair or destroy a circuit's performance. Yet a person walking on carpet on a dry day can accumulate as much as 30,000 volts of potential, and he or she can triboelectrically generate thousands of volts by simply changing his or her position in a chair or handling a styrofoam cup.
Such a person can inadvertently discharge such static potential into a circuit or component by touching it and causing over-voltage or excessive power density. Additionally, the potential in such a person's body can induce a charge in a circuit that can later cause over-voltage or excessive power density when the circuit is subsequently grounded.
Those in industries in which integrated circuits and other microelectronic components are handled or assembled may take measures to limit the failure rate of those circuits and components by attempting to keep them as well as their environment at zero electrical potential. Such measures include providing workers and work stations with electrostatic discharge (ESD) devices, such as antistatic carpet, conductive or dissipative grounded desk top work surfaces, hot air ion generators which emit ions to neutralize static changes, grounding wrist straps, heel grounders and other garments to keep workers at zero potential.
The situations in which grounding wrist straps are used heighten the importance of their being effective, reliable, and predictable. The person working on microelectric components or integrated circuits may be completely unaware that he or she has accumulated minor static electrical charges, and may therefore unknowingly be in a position to disable circuits on which he or she is working or which he or she is handling. If the strap is loose or has been removed or if it is not functioning properly for other reasons, the worker may be unaware that electrical discharges transmitted from his or her fingers are disabling the circuits. (A typical person cannot sense a static electrical discharge of less than approximately 3,500 volts.) No one may discover that the circuits have been disabled or damaged until hours, days or weeks later, when the circuits have been placed in components or devices which fail in the field. Removal and repair or replacement of these circuits once in the field is far costlier than avoiding potential failure while the worker is handling the circuits.
Various procedures for ensuring the proper use and efficacy of ESD devices have been developed. For instance, wrist strap or heel grounder testers have been developed which allow a worker to verify the efficacy of the device. These testing units may be used periodically to monitor the efficacy of the ESD device. In other words, each work area may have an ESD device testing unit with which each worker verifies his or her ESD device(s) prior to beginning a shift or at other predetermined intervals.
Such testing units are of little value, however, if they are not used in a manner which creates confidence that the ESD devices are being tested frequently and consistently enough to ensure reliable function. Thus, protocols may be established for periodic testing or auditing of the ESD devices. For instance, ISO 9000 standards require that any claims that products are manufactured under ESD controlled conditions be verifiable through documentation. Thus, workers must record their use of the devices and periodically verify their efficacy with test equipment. These records are then used to certify the products under the standard. Other industry standards or internal operating procedures also may require documentation of ESD auditing programs.
One problem created by conventional methods for recording and tracking of ESD auditing programs is the generation of large amounts of printed documents or records. Such documentation is, however, required for many manufacturing processes. These records can be bulky and so voluminous that they are practically useless for analytical purposes. Thus, in order to provide the data that can be used in meaningful ways, the records must be entered by hand into a computer database--an expensive and time consuming process. Furthermore, maintaining such records by hand can introduce errors resulting from mis-recording or worker inattention.
Moreover, the conventional method of recording ESD data, i.e., by hand, typically fails to record data which may be particularly useful in establishing, monitoring and improving an ESD auditing program and the ESD devices themselves. For instance, if the test of a wrist strap or other ESD device fails, the worker typically adjusts the device and re-tests, repeating the process until a satisfactory test result is achieved. The user then records the fact that the test was performed and passed and proceeds to a work station. The records do not reflect, however, the fact that several tries may have been necessary in order to pass the test. This information is valuable because it can give statistical information as to the reliability and durability of the ESD device.
Another limitation of manual data entry is the lack of real-time availability of the data to the program supervisor. Currently, if a supervisor wishes to determine whether all ESD devices have been properly tested according to program requirements, he or she must go to each testing station and examine the log book. In a large fabrication facility, the examination of each log book may be difficult or even impossible to do in a short time.